In Greek mythology, a Nereid loved by both Zeus and Poseidon. When it was revealed that Thetis was destined to bear a son who would be mightier than his father, the two gods gave her to Peleus, king of the Myrmidons. Unwilling to wed a mortal, Thetis resisted Peleus' advances by changing into various shapes, but Peleus finally captured and married her. Their child was Achilles. Some legends relate that she bore seven children, all of whom perished either when she tried to render them immortal or when she killed them as the offspring of a forced marriage.